1. Field of the Invention
The present invention relates to a circuit arrangement for checking the quality of electrical contact between a transmitter circuit and a receiver circuit.
2. Description of the Prior Art
The transmission of electrical signals between a transmitter circuit and a receiver circuit generally takes place along conductors. The conductors are normally provided at their ends with terminals or connectors which enable contact to be made or not to be made between the transmitter and the receiver via the conductor which connects them. In many cases, the transmitter and receiver are fixed components which are in contact either permanently or for comparatively long periods of time. It is therefore generally satisfactory to ensure that there is good contact between the two components at the start of a signal-transfer operation to be carried out. When contact between the two ends of the conductor is made by plugging in pins of relatively large dimensions, the interference caused by dust or other contamination of an insulating nature is not troublesome and in this case there is no need to check the standard of contact.
Quite the opposite is true if a pin of small dimensions is badly inserted, because of the presence of dirt for example at the bottom of the socket into which the pin is inserted, and makes poor contact, which will be detrimental to the operations which would normally be performed with the signals received by the receiver. A check on contact becomes all the more necessary if the receiver involved is a portable one which is often moved and is set up in places where there is little protection from dirt. The problem of the quality of contact is even more critical when the transmitted signals are in the form of brief pulses emitted at relatively high frequency. In this case, dirt at the point where the pin makes contact may give rise under the conditions of pulsed transmission envisaged above, to a not inconsiderable stray capacity effect, and because of this, certain of the pulses emitted by the transmitter may be lost at the input to the receiver.
This possibility must be kept in mind particularly in cases where the transmitter and receiver circuits are logic circuits made up of discrete or integrated components. Links between such circuits are intended for an exchange of digital data in which pulses are transmitted from one circuit to the other at a given rate. In cases where the data exchanged has to be processed in synchronization in both circuits, a conductor is set aside to transmit so-called "clock" pulses to ensure this synchronization. In this example of an application of a contact inserted between two logic circuits to transmit either clock pulses or pulses representing digital data, it is important to measure the quality of contact during the whole time pulses are being transmitted, thus providing an assurance of the validity of the data exchanged and of the synchronous operation of the circuits.
A widely used method consists in checking the quality of contact between a transmitter circuit and a receiver circuit by measuring the voltage at the input to the receiver. If the contact is good, the voltage received at the input of the receiver is a predetermined function of the voltage measured at the output from the transmitter.
Another method envisions the use of a portable card for systems for processing electrical signals. In this case, the electrical contacts between a portable card and a data-processing system are made by pins which are inserted into cut-outs formed in the card until they reach terminal areas of conductors which are directly linked to a signal-processing receiver device. A predetermined voltage is applied between two electrodes which are inserted in two contact cut-outs which face a terminal area of one and the same conductor which is connected to the receiver and/or transmitter device. Contact is satisfactory if a predetermined current is found to flow between the two cut-outs and the terminal area.
Although this latter method is a simple way of carrying out an effective check on contacts such as those which exist at a portable card which may be a signal transmitter or receiver, the means which it employs are more suited to performing a check before the card is connected to a data-processing system. These means would in fact have the disadvantage of being too bulky to be left permanently attached to the card, particularly in cases where the card is a credit card of standard dimensions. Furthermore, in this particular case, it is necessary to check the quality of contact at the card when the contact is providing an electrical link to the card with the latter operating as a receiver. When the card is transmitting signals to the data-processing system through a contact made at the card, the quality of contact can be checked at the system by known means which are easily put into operation and which may consist for example in checking the received data by software means.
One of the objects of the invention is to provide permanent checking means which operate for the whole time during which signals are being transmitted from a transmitter to a receiver.
Another object of the invention is to provide means which do away with the need to perform a check at the input to a receiver.